Solar energy collectors are well-known in the art. They are varied in type but generally consist of devices which absorb the sun's energy, convert it to heat or directly to electrical energy and transmit the energy to a point of use or storage.
This invention relates to a heat type of energy collector and more particularly to a collector consisting of an insulated enclosure having a transparent wall with a "black body" planar heat collecting member therein such as is described in applicant's co-pending application, Ser. No. 659,259, filed Feb. 19, 1976.
In the prior art, economical construction of such solar energy collectors with large areas has been difficult to achieve. This is due, in part, to the large degree of expansion and contraction that takes place within the collector, particularly in the heat or energy absorbing member. To keep these dimensional changes within the bounds of simple and reliable construction the perimeter dimensions of the collectors have generally been kept small. This results in higher costs for a large total area since many small collectors must be used with an accompanying large sum of linear perimeter feet of all the individual collectors.
A major step toward reducing an installation cost is to reduce the number of collectors needed by using a small number of very large collectors in place of many small collectors. This can be achieved by designing the collector assembly so that its structural and functional integrity is not affected by the larger dimensional changes that inherently occur as the collector size increases.
This invention provides a technique for mounting large energy collecting members in solar energy collectors by using a single thin heat absorbing sheet attached to an outer frame with tension devices to maintain the member in a planar configuration, regardless of the dimensional state of the collecting member.
Where liquid is used to transmit the energy from the member, liquid will flow down the back surface of the planar member. The perimeter of the member must have attached a vapor-tight seal, in this case, to prevent moisture or moist vapor from reaching the volume of air in front of the sheet. Where a gas is used to transmit the energy the member must also be basically planar but may have thin heat exchanger fins attached to facilitate heat removal. Where a gas is used as a transmitter, internal type seals are not required. With the use of the proper materials and elastic tension hardware, the assembly size is limited only by handling and transportation requirements, thereby substantially reducing the cost of installation.
Utilization of an extremely thin sheet for a collecting member also provides benefits in that the cost of the collecting member is reduced (less material and standard, off-the-shelf stock may be used), extremely large collecting members can be transported in a rolled condition and selective surface coatings can be applied, where desired, in a continuous coating process rather than the batch coating processes now required with thick, rigid collecting members.
Since the member is essentially isolated from external forces by the surrounding frame and insulating enclosure of the collector, it need only be thick enough to have the strength to withstand the tensile load.